1. Field of the Invention
The present invention relates to a silicone-sealed LED using a silicone resin as a sealing material, and in particular, relates to a silicone-sealed LED provided with a buffer layer comprising silicone rubber between the silicone resin seal and the LED chip. The present invention also relates to a process for producing the silicone-sealed LED and a process for sealing a LED.
2. Description of the Prior Art
Epoxy resins are generally used as the sealing materials for light emitting diode elements. However, because epoxy resins have a high modulus of elasticity, the resulting distortions which occur during temperature cycling due to the different coefficients of linear expansion for the wire, the chip, and the epoxy resin mean stress acts on the wire bonding, and as a result, cracks can occur in the sealing body comprising the resin, disconnecting the wire bonding. Consequently, as a result of the stress applied by the epoxy resin seal body to the LED chip, there is a danger of the crystal structure of the LED chip being destroyed, decreasing the luminous efficiency of the LED.
As a countermeasure to these problems, a method using a rubber-like silicone RTV as a buffer material, wherein the exterior thereof is sealed with an epoxy resin, is now established as an accepted method. However, with this method, because the epoxy resin does not adhere to the silicone resin, interfacial peeling occurs on temperature cycling, considerably decreasing the light extraction efficiency over time.
On the other hand, sealing using silicone resins instead of epoxy resins has also been proposed as a method of resolving the aforementioned problems (patent references 1 to 3). Because silicone resins exhibit superior heat resistance, weather resistance and color fastness and the like when compared with epoxy resins, in recent years, examples using silicone resins, primarily with blue and white LEDs, have become prevalent. However, although silicone resins have a low modulus of elasticity compared to epoxy resins, the mechanical properties such as the flexural strength are inferior, leaving the problem of a tendency for cracks to occur.
[Patent Reference 1] JP 11-1619A
[Patent Reference 2] US 2002/0161140 A1
[Patent Reference 3] US 2004/0116640 A1